Not Applicable
Not Applicable
The present invention is directed to an apparatus for electrochemically processing a microelectronic workpiece. More particularly, the present invention is directed to a reactor assembly for electrochemically depositing, electrochemically removing and/or electrochemically altering the characteristics of a thin film material, like a metal or dielectric, at the surface of a microelectronic workpiece, such as a semiconductor wafer.
For purposes of the present application, a microelectronic workpiece is defined to include a workpiece formed from a substrate upon which microelectronic circuits or components, data storage elements or layers, and/or micro-mechanical elements are formed.
Production of semiconductor integrated circuits and other microelectronic devices from microelectronic workpieces, such as semiconductor wafers, typically requires the formation and/or electrochemical processing of one or more thin film layers on the workpiece. Electroplating and other electrochemical processes, such as electropolishing, electro-etching, anodization, etc., have become important in the production of semiconductor integrated circuits and other microelectronic devices from such workpieces. For example, electroplating is often used in the formation of one or more metal layers on the workpiece. These metal layers are typically used to electrically interconnect the various devices of the integrated circuit. Further, the structures formed from the metal layers may constitute microelectronic devices such as read/write heads, etc. Such electrochemical processing techniques can be used in the deposition and/or alteration of blanket metal layers, blanket dielectric layers, patterned metal layers, and patterned dielectric layers.
The microelectronic manufacturing industry has applied a wide range of thin film layer materials to form such microelectronic structures. These thin film materials include metals and metal alloys such as, for example, nickel, tungsten, tantalum, solder, platinum, copper, copper-zinc, etc., as well as dielectric materials, such as metal oxides, semiconductor oxides, and perovskite materials.
Although the following discussion and subsequent embodiment of the present invention is described in the context of electroplating, it will be recognized that the teachings herein can be extended to other electrochemical processing techniques in which at least two electrodes are used. To this end, the electroplating of a microelectronic workpiece generally takes place in a reactor assembly. In such a reactor assembly, an anode electrode is disposed in a plating bath, and the workpiece with the seed layer thereon is used as a cathode. Only a lower face of the workpiece contacts the surface of the plating bath. The workpiece is held by a support system that may also include electrically conductive members that provide the requisite electroplating power (e.g., cathode current) to the workpiece.
Generally stated, electrochemical processing occurs as a result of an electrochemical reaction that takes place at the surface of the workpiece. In electroplating, for example, atoms of the material to be plated are deposited onto the workpiece, which functions as a cathode, by introducing an external electrical power source that supplies electrons to attract positively charged ions. The atoms are formed from ions present in the plating bath. In order to sustain the reaction, the ions in the plating bath must be replenished. Such replenishment may include the use of a consumable anode that releases the desired bath species as it is depleted from the bath.
When electroplating copper onto a workpiece, replenishment of the copper ions in the plating bath may be accomplished, at least in part, through the use of a consumable phosphorized copper anode. As copper ions are depleted from the plating bath, a corresponding number of copper ions are released by the anode into the plating bath. Other chemicals that are depleted during the electroplating process may be replenished by controlled dosing of the bath with one or more bath additives.
As the thin film layer is deposited onto the cathode, a related electrochemical oxidation reaction takes place at the anode. During this related electrochemical reaction, byproducts from the electrochemical reaction, such as particulates, precipitates, gas bubbles, etc., may be formed at the surface of the anode. Such byproducts may contaminate the processing bath and interfere with the formation of the thin-film layer at the surface of the workpiece. Furthermore, if these byproducts are allowed to remain in the plating bath at elevated levels near the anode, they may affect electrical current flow during the plating process and/or affect further reactions that take place at the anode. Still further, if the byproducts are allowed to migrate proximate the microelectronic workpiece, the byproducts could similarly interfere with the desired deposition of electroplated material thereby affecting the uniformity of the thickness of the deposited material.
Such byproducts can be particularly problematic in those instances in which the anode is consumable. For example, when copper is electroplated onto a workpiece using a consumable phosphorized copper anode, a black anode film is produced. The presence and consistency of the black film is important to ensure uniform anode erosion. This oxide/salt film is fragile, however. As such, it is possible to dislodge particulates from this black film into the electroplating solution. These particulates can then potentially be incorporated into the deposited film with undesired consequences.
A further consideration with respect to processes that use a consumable anode is erosion of the anode. Specifically, as the anode erodes, the distance between the anode and the cathode gradually increases. Furthermore, the overall shape of the anode as viewed by the workpiece changes. Such erosion, in turn, affects the strength and shape of the electric field formed between the anode and the cathode, thereby altering the deposition of material onto the surface of the microelectronic workpiece. Still further, consumable anodes erode to the point where they eventually need to be replaced.
Processes that do not make use of a consumable anode have also been developed. Generally, in these processes an inert anode is used in place of the consumable anode. Where the consumable anode, can provide a source for ions in the plating bath, an inert anode generally does not supply ions to the plating bath. In processes that use an inert anode, ions in the plating bath are generally replenished from the flow of fresh chemistry into the plating reactor. The plating solution containing fresh chemistry generally displaces the plating solution from which plating ions have been depleted. Consequently, the concentration of plating ions within the plating bath is largely affected by the flow of fresh plating solution within the plating reactor.
However the flow of plating solution is seldom uniform. The uniformity of the flow of fresh plating solution within the plating reactor can be affected by several different factors. One such factor includes the size, shape and position of the fluid inlet and the fluid outlet, which defines the starting point and the ending point for the fluid entering and or exiting the reactor. A further factor includes the size, shape and position of elements within the plating reactor, which may limit or obstruct fluid flow within the plating reactor, thereby altering the path of the fluid flow within the plating reactor. For example an object within the plating reactor may force fluid to be diverted around the object resulting in the fluid flow being more narrowly channeled around the outer periphery of the object. Additionally, this may result in the creation of dead spots within the chamber around which the fluid has been diverted and where the processing fluid remains relatively stagnant. This can result in localized areas where replenishment of the processing fluid and the corresponding concentration of fresh plating ions is affected thereby resulting in non-uniformity of the deposited film.
One factor that can affect the rate at which a material is electroplated onto a workpiece is the concentration of the ion species proximate the surface of the workpiece. As ions are consumed or plated out of the plating solution proximate a particular location on the surface of the workpiece, the ions need to be replaced or replenished to insure ions are available for continued plating of the material onto the surface of the workpiece. To the extent that the ions necessary for further plating are not replenished, the rate of reaction at the surface of the microelectronic workpiece will suffer. Local differences in the rate of plating can result in undesirable non-uniformity of the overall plated layer.
Still further, a related electrochemical oxidation reaction takes place proximate the inert anode. This related reaction similarly requires that certain ions be present and continuously replenished for the related reaction to continue at the anode in the desirable manner. For example, in the absence of a suitable reducing agent proximate the anode, water in the plating bath may be oxidized resulting in gas bubbles at the anode. This may contaminate the processing bath and interfere with the formation of the thin film layer at the surface of the microelectronic workpiece. Additionally, the related reaction at the anode may be impacted by local concentrations of ions in the plating solution and the corresponding fluid flow proximate portions of the anode.
The present inventors have recognized the foregoing problems and have developed a reactor for electrochemically processing a microelectronic workpiece that manages the flow of electrochemical processing solution within the reactor so as to provide for a generally uniform flow of processing solution throughout. Flow of the electrochemical processing solution is controlled proximate the workpiece as well as proximate the anode. Such control provides for a more even distribution in the concentration of reactants required for the electrochemical processing reactions at the anode and the cathode. In this way, uniform electrochemical processing, such as the electrolytic deposition of material onto a microelectronic workpiece, can be achieved.
A reactor assembly for electrochemically processing a microelectronic workpiece is set forth. The reactor assembly includes a processing bowl having one or more fluid inlets through which a flow of processing fluid is received. An electrode assembly is located within the process bowl in a fluid flow path of the fluid provided through the one or more fluid inlets. The electrode assembly includes a mesh electrode and a diffuser disposed in the fluid flow path prior to the mesh electrode to tailor the flow of processing fluid received from the one or more fluid inlets through the mesh electrode in a predetermined manner.
In accordance with one embodiment of the invention, the diffuser is formed as a separate component from the mesh electrode. The diffuser is disposed between the one or more fluid inlets and the mesh electrode to tailor the flow of processing fluid traveling between the one or more fluid inlets and the mesh electrode. In accordance with another embodiment the diffuser is integral with the mesh electrode. The reactor may also include an electrode support assembly that is dimensioned to direct substantially all of the processing fluid received through the one or more fluid inlets toward the mesh electrode.
A further diffuser may also be employed between a portion of the fluid flow path between the mesh electrode and the microelectronic workpiece. Optionally, the further diffuser may be constructed so that the flow therethrough optimizes the conditions under which the fluid contact the mesh electrode. This assists in ensuring that the fluid and mesh anode are in contact with one another under conditions that allow the completion of any reactions between them before the fluid is provided for contact with contact the microelectronic workpiece being processed. Alternatively, or in addition, a pump that is used to supply the fluid to the reactor chamber may control such flow.
Various constructions of the mesh electrode are also set forth. Further, an integrated tool including a reactor constructed in accordance with one embodiment of the present invention is set forth.